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Chapter 5 Programming Considerations
© National Instruments Corporation 5-35 VXI-MXI User Manual
Multiframe RM Operation
On power-up, all MXIbus devices are isolated from each other because all address mapping
windows are disabled. The multiframe RM performs the following:
• Identifies all devices in the system
• Manages system self-tests
• Configures and enables the address map windows for logical addresses, A16, A24, and A32
• Establishes initial Commander/Servant system hierarchy
• Initiates normal system operation
Configuring the Logical Address Window
To identify all devices in the VXIbus/MXIbus system, the RM performs the following steps,
starting where the RM is located.
1. If the multiframe RM resides in a PC, it scans all logical addresses from 1 to FE (the RM is at
address 0) to find all devices. For each logical address, it reads the VXIbus ID Register
(located at offset 0 within the device's configuration space). If the read is successful (that is,
no BERR), a device is present at that logical address. If the read returns a BERR, no device
is present at that logical address. The RM records all logical addresses found. For each
VXI-MXI found, it performs Step 2.
If the multiframe RM is in a VXIbus mainframe, it performs Step 2 for the mainframe in
which the RM is installed.
2. For the current mainframe, the RM does the following:
A. Scans all logical addresses (0 to FF) in the mainframe to find all static configuration (SC)
and dynamic configuration (DC) devices, skipping over logical addresses occupied by
previously encountered devices. Finds the Slot 0 device and uses it to move all DC
devices in the mainframe to the lowest unused logical addresses. Records all logical
addresses found and allocated.
Notice that it is not possible to detect duplicate logical addresses because devices are
found by reading the VXIbus ID Register. If two devices share a logical address, they
will both respond to an address access without any indication of an error.
B. For each VXI-MXI found in the mainframe, starting with the lowest addressed VXI-MXI,
the RM:
i. Sets the VXI-MXI logical address window to map all of the logical address space
outward and enables the window.
ii. Scans all logical addresses (0 to FF) in the window, skipping logical addresses
occupied by previously encountered devices.
iii. For each VXI-MXI found in Step ii, starting with the lowest addressed VXI-MXI,
the RM:
a. Sets the VXI-MXI logical address mapping window to map all of the logical
address space inward and enables the window.